Bilayer glazing panel

ABSTRACT

A wrinkle-free bilayer glazing panel comprising sequentially: a) a sheet of glass; b) a layer of plasticized partial polyvinyl butyral; c) a transparent polyester layer; and d) a layer of cross-linked, self-healing polyurethane.

BACKGROUND OF THE INVENTION

This invention relates to bilayer glazing panels and more particularlyto such panels which include plasticized polyvinyl butyral andpolyurethane as components.

Laminated glazing panels are well known for use as windshields, side andrear windows, and sunroofs in vehicles, architectural glass in buildingsincluding skylights, intrusion security glass, solarium doors and thelike. Along with glass, these panels include an energy absorbing plasticlayer capable of absorbing a blow from an object without penetration ofthe glazing panel by the object, thus providing safety to occupants ofthe surrounding area.

Commercial laminated glazing panels usually have a pane of glass on eachside of the energy-absorbing layer. An alternative to this trilayerstructure is a bilayer which has a single pane of glass against aplastic inner layer usually of two or more plies. In addition to beinglighter in weight, when impact sufficient to break the glass of abilayer occurs, the danger from glass fragments within a room or vehiclecompartment is greatly reduced by the absence of the interior glasslayer.

Plasticized polyvinyl butyral is used most as the energy-absorbing layerin the trilayer structures mentioned above. Such polyvinyl butyralcontains about 15-30 weight % hydroxyl expressed as polyvinyl alcohol,("partial PVB") for interaction with the glass to form a tenacious bondin the laminate (along with 0 to 2.5 weight % acetate expressed aspolyvinyl acetate with the balance being butyral expressed as polyvinylbutyral). Because of long commercial use in trilayer glazing panels,laminators are quite familiar with the handling and properties ofplasticized partial PVB sheet, and it has been proposed for use inbilayers. U.S. Pat. No. 4,937,147 focuses on the bond between partialPVB and polyurethane in a bilayer and U.S. Pat. No. 4,952,457 on themoisture tolerance of plasticized partial PVB sheet in a bilayer. Asdisclosed in these patents, it is likewise known to use cross-linkedpolyurethane in bilayers as the damage-resistant inboard surface facingthe interior of the vehicle compartment or room containing the bilayer.

While moderately successful, the systems of these patents deal withproperties of the plastic components of a bilayer and do not addresseconomical preparation of bilayers on a commercial scale.

SUMMARY OF THE INVENTION

Now, improvements have been made to fulfill a prior art need forcommercially attractive systems for preparing bilayer glazing panels.

Accordingly, a principal object of this invention is to provide a methodand apparatus for preparing a bilayer glazing panel.

Another object is to provide a commercially significant, tractable,method and apparatus for preparing such a panel.

A further object is to provide improvements in bilayer glazing panelswhich use partial PVB and polyurethane as structural components.

Other objects of this invention will in part be obvious and will in partappear from the following description and claims.

These and other objects are accomplished by providing a wrinkle-freebilayer glazing panel comprising sequentially a) a sheet of glass; b) alayer of plasticized partial polyvinyl butyral; c) a transparentpolyester layer; and d) a layer of cross-linked, self-healingpolyurethane.

BRIEF DESCRIPTION OF THE DRAWINGS

In describing the overall invention, reference will be made to theaccompanying drawings wherein:

FIG. 1 is a flow diagram of an apparatus assembly according to theinvention;

FIG. 2 is a plan view of an apparatus component of FIG. 1;

FIG. 3 is a sectional view along 3--3 of FIG. 2;

FIG. 4 is a partial, sectional view of an alternate embodiment of FIG.3;

FIG. 5 is a sectional view in enlarged detail of a portion of theplastic layers during a forming step of the invention; and

FIG. 6 is a view similar to FIG. 5 of a bilayer glazing panel of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, apparatus collectively identified as 10is shown in FIG. 1 for forming bilayer glazing panel 100 (FIG. 5).Apparatus 10 comprises air autoclave chamber 12 defined by walls,illustratively shown as 13, of sufficient strength to withstandsignificant vacuum and pressure developed during the bonding process tobe later described. At least one and preferably plural thermoformingassemblies 14a, 14b, 14c are housed within chamber 12. An appropriateopenable and closeable means of access (not shown) to chamber 12 isprovided in walls 13 for servicing thermoforming assemblies 14, such as,for example, a sealable hinged access door.

Each thermoforming assembly 14 (FIGS. 2 and 3) comprises a perimeteranchoring system 16 for a layered composite sheet to be furtherdescribed, a support bed 18 within the periphery of perimeter anchoringsystem 16 and means 20 (FIG. 1) associated with support bed 18 forimposing a vacuum on a thermoforming assembly 14. Means 20 comprisesopening 22 (FIG. 3) in upstanding sidewall 24 which is rigidly securedto base 28 to form shallow cylindrical housing 26 (FIG. 2). Opening 22of means 20 in sidewall 24 of housing 26 of each thermoforming assembly14 communicates via conduits 29a, 29b, 29c (FIG. 1) with vacuum pump 30.When plural thermoforming assemblies 14 are used, each opening 22 isconnected to conduits 29 through manifold 27.

As distinguished from means 20, means 34 (FIG. 1) is provided forcreating vacuum within autoclave chamber 12 and comprises conduit 36communicating at one end 38 with the interior of chamber 12 and atanother end with vacuum pump 30.

Apparatus 10 further comprises (FIG. 1) means 40 for controllablyheating the atmosphere within autoclave chamber 12 which isillustratively shown as electrically conductive heating coil assembly 42and circulating air fan 44 within chamber 12. Coil 42 is conventionallyoperatively electrically connected with a power source, not shown.

Support surface 46 of support bed 18 (Fig 3) has yieldable bearing layer48 secured thereto formed, for example, of an elastomeric material suchas silicone rubber and contoured as shown to match the surface profileof glass layer 102.

Each perimeter anchoring system 16 (FIG. 3) includes sealing ring 49 andplural threaded knobs 50a, 50b evenly spaced around the perimeter ofhousing 26 which are swingably moveable in arrowed direction 52 into andout of engagement with ring 49 via pivotal attachment at 54 to a bracketsecured to sidewall 24 of housing 26.

Tapped bore 56 on the vertical axis of support bed 18 within housing 26cooperatively engages threads 58 of member 60 fastened by bolts 62 tobase 28. The vertical position of support bed 18 within housing 26 isset by rotating bed 18 to cause cooperative up or down movement ofthreads 59 along threads 58 Plural peripherally spaced, horizontallyadjustable positioning bolts 64 center support bed 18 concentricallywithin cylindrical housing 26 via engagement with the inner surface ofsidewall 24. For non-circular (e.g. rectangular) configurations ofsupport bed, enclosing housing and cooperating perimeter anchoringsystem, the support bed is vertically positioned by an alternative meanssuch as shim stock between the bed and the base of the housing.

Means 66 (FIG. 1) comprising air compressor 68 communicating at 70 withautoclave chamber 12 through line 72 containing control valve 74 createspositive pressure within chamber 12 at the appropriate stage of theforming process

Each thermoforming assembly 14 is removably seated on an appropriatesupport shelf not shown, or, alternatively, stacked one upon the otherin one or more stacks within chamber 12.

In the FIG. 4 embodiment, where like numerals identify components havingthe same numbers in FIGS. 2, 3, thermoforming assembly 14 optionallyincludes spacer 76 between sidewall 24 and support bed 18 having weephole 77 to provide communication between vacuum opening 22 and supportbed 18. Contoured surface 78 of spacer 76 supporting region 79 oflayered composite 32 avoids any large unsupported areas during shapingwhich if present might rupture the composite. Spacer 76 of appropriateshape and peripheral extent could be used, for example, when a singlecommon housing 26 is used to accommodate different peripheral bilayershapes and, accordingly, different contours of support bed 18. Thus,when a particular bilayer configuration is being formed with such acommon housing, spacer 76 could be used to avoid such substantialunsupported area as just described, whereas for a peripherally largerconfiguration as shown in FIG. 3, it could be removed as unnecessary.

The method will now be described for forming bilayer glazing panel 100(FIG. 5) of glass and plastic using apparatus 10.

The optically clear prelaminate presented to apparatus 10 forfabrication with glass into a bilayer glazing panel comprises astretched polyester, such as polyethylene terephthalate (PET), filmcoated with cross-linked, self healing polyurethane (PU) and optionallytreated or coated on the reverse side to promote adhesion particularlyto plasticized partial PVB. Prelaminate formation is described laterherein.

The prelaminate is assembled with a layer of plasticized partial PVBwith the side of the PET without the PU facing a subjacent surface ofthe plasticized partial PVB layer. This assembly is collectivelyschematically shown as layered composite 32 in FIG. 3 and in detail inFIG. 5 where 80 is the plasticized partial PVB layer, 82 is the PETlayer and 84 the PU layer. Surface 86 of PET layer 82 bears PU layer 84and surface 88 of layer 82 is in face-to-face contact with preferablytextured, subjacent side 90 of plasticized partial PVB layer 80. Pluralspaced deairing holes 92 (FIG. 5) extend completely through thethickness of plasticized PVB layer 80 outside (FIG. 2) the area of layer80 to be used in the bilayer glazing panel. The open size of holes 92 isnot critical and can be determined by simple experiment. Openings ofabout 3 to 10 mm have been used successfully and may be formed manuallyin the soft PVB material or, for example, by passing layer 80 over apowered cylinder provided with sharp projections to pierce the sheet, orby some alternate equivalent means.

Deairing holes 92 communicate with the interface between layers 80 and82. Instead of such holes, an alternative means associated with theapparatus could be provided for deairing this interface such as, forexample, a separate deairing ring, not shown, opposite the interfacebetween clamping ring 49 and the top of sidewall 24 having ports throughwhich a vacuum could be drawn on such interface.

Assembly 32 of plastic layers is clamped within perimeter anchoringsystem 16 in the substantially horizontal attitude shown in FIG. 3.Clamping between sealing ring 49 and the top face of sidewall 24 isachieved by pivoting each knob 50 into the FIG. 3 position and thenturning it downwardly to compressively engage the illustrated washerwith the sealing ring surface as shown.

After sealing autoclave chamber 12 shut, the following steps are thencarried out sequentially, preferably in an automated manner. The valvesbetween vacuum pump 30 and opening 38 of means 20 (FIG. 1) are openedand pump 30 energized to impose a vacuum within autoclave chamber 12.Valve 31 of the means for imposing vacuum on a thermoforming assembly 14is opened to also selectively create essentially the same vacuum throughopening 22 on the underside of the layered composite 32 clamped withinanchoring system 16. Though composite 32 may be optionally heated tofacilitate drawing, it is preferably unheated at this stage of theprocess. The vacuum on the underside of composite 32 sealed withinassembly 16 causes air to be expelled through holes 92 in lowermostplasticized PVB layer 80 thereby deairing the interface between PETlayer 82 and plasticized PVB layer 80 while, as in FIG. 3, composite 32remains essentially horizontal because of the equal vacuum abovecomposite 32 imposed through port 38. Vacuum pump 30 is then deenergizedand compressor 68 engaged to gradually (via control valve 74) develop apressure differential across the deaired assembly of plastic layers toforce localized regions (94 in FIG. 3) within the periphery of theperimeter anchoring system and inward of deairing holes 92 in PVB layer80 against the surface of an underlying transparent sheet 102 of floatglass previously positioned on the break-resistant surface of yieldablelayer 48. The drawn position of layered composite 32 after region 94engages glass layer 102 is approximately shown as within dotted lines 96in FIG. 3. While the plastic layers are essentially in dotted lineposition 96 and continue clamped within perimeter anchoring system 16,the temperature and pressure within chamber 12 are increased to levelswhich are maintained for a period of time adequate to firmly bondplasticized partial PVB layer 80 to glass layer 102 through interactionwith the polyvinyl alcohol groups of the partial PVB layer, as well asto melt bond polyethylene terephthalate layer 82 to partial PVB layer80. Air at elevated temperature is provided by energizing coil 42(FIG. 1) and circulated within chamber 12 via fan 44. Using compressor68 and control valve 74, pressure within chamber 12 is graduallycontrollably increased to the desired level. As such pressure isincreasing, differential pressure control value 98 functions to maintainthe pressure on the underside of drawn composite 96 being imposed on anassembly 14 through port 22, incrementally below the increasingautoclave pressure being developed on the top side of the drawncomposite. This is accomplished by providing for control valve 98 tocontrollably open to gradually increase pressure within a thermoformingassembly 14 through lines 29, (FIG. 1), valve 37 being open. Thisfeature helps to avoid any tendency of the drawn, clamped composite torupture in the region where it overhangs bearing layer 48 inward ofsealing ring 49 or of the glass to fracture.

Autoclave conditions for creating the desired bond between the partialPVB and glass layers are about 140° C. and 1135 kPa for about 30minutes.

After reducing conditions within chamber 12 to atmospheric, removing thelaminate from assembly 14 and trimming away unwanted plastic portionsoutside the periphery of glass layer 102, the product of the process iswrinkle-free bilayer glazing panel 100 (FIG. 6) comprising sequentially,glass sheet 102, shaped layer 104 of plasticized, partial PVB firmlybonded to glass layer 102, transparent polyester film 106 and layer 108of cross-linked, self-healing polyurethane. As illustrated in FIG. 3,glass sheet 102 (and therefore bilayer glazing panel 100) preferably hascompound curvature by which is meant that some degree of stretching ofthe flat, planar thermoplastic layers of composite 32 is necessary inconforming such thermoplastic layers into surface contact with thecompound curvature surface. Alternatively a flat sheet of glass may beused to produce a substantially planar bilayer glazing panel which maybe quite adequate, for example, as a side window in a motor vehicle.

Preparation of an optically clear prelaminate of polyester andpolyurethane for processing in apparatus 10 will now be described. Thepolyester is stretched film, preferably optically clear biaxiallystretched polyethylene terephthalate film about 0.0125 to 0.175 mm thickoptionally coated, such as with a pressure sensitive adhesive, ortreated such as by plasma, flame, corona, glow discharge or the like, onone or both sides, to promote adhesion and specifically to promoteadhesion to plasticized partial PVB. Such polyethylene terephthalatecontains repeating units of ethylene terephthalate and includescopolymers of ethylene terephthalate where up to about 10 mole percentof the esterifying glycol units are derived from diethylene glycol;propane-1,3-diol; butane - 1,4 diol; polytetramethylene glycol;polyethylene glycol and the like and up to about 10 mole percent of theacid component is derived from acids such as isophthalic; dibenzoic;naphthalene 1,4 - or 2,6 - dicarboxylic; adipic; sebacic and the like.

The polyester film is coated with transparent, cross-linkablepolyurethane which is usually, but not necessarily, a single layer. Thechemical structure of the polyurethane can vary widely provided thatafter curing a cross-linked, self-healing surface is obtained which iscapable of damage-resistant, non-yellowing performance as the innerexposed surface of a bilayer glazing panel--i.e. facing the occupant ofa vehicle or room containing the bilayer panel as a window. Preferredpolyurethane compositions and performance-enhancing additives, tailoredas hereinafter described as may be necessary for use with polyestersubstrates, are disclosed in U.S. Pat. No. 4,937,147, col. 4, line 45through col. 7, line 20, U.S. Pat. No. 4,923,757, col. 3, line 45through col. 5, line 37 and U.S. Pat. No. 4,925,734, col. 4, line 31 andcol. 5, line 30, the noted content of which is incorporated herein byreference.

Plasticized partial PVB sheet at a thickness of about 0.25 to 1.5,preferably about 0.35 to 0.75 mm, is commercially available fromMonsanto Company as Saflex® sheet and E. I. duPont de Nemours & L.Company as Butacite® polyvinyl butyral resin sheeting. As commerciallysupplied, such sheet contains plasticizer and is textured or roughenedon each of its major side surfaces. Plasticizers for partial polyvinylbutyral are well known and disclosed in U.S. Pat. No. 4,902,464, col. 5,lines 11-21, the content of which is incorporated herein by reference;techniques for texturing the surface of plasticized partial PVB sheetare likewise known disclosed in U.S. Nos. 2,904,844; 2,909,810;3,994,654; 4,575,540 and European Patent No. 0185,863, the content ofwhich is likewise incorporated herein by reference.

The PU composition is applied to the polyester film by rolling,spraying, casting, spinning, extrusion, rod or blade coating, slide orcascade coating or the like. For ease of large scale application,curtain coating is preferred.

Commercially available, self-contained curtain coating systems areusable. In a typical system the ingredients are mixed in a stirredvessel and pumped through a filter to a coating head disposed above areceiving trough extending perpendicular to the forward direction ofmovement of feed and take-away conveyors supporting the substrate beingcoated. The trough is fed by gravity from the coating head and a liquidcurtain of the PU formulation issues through an adjustable gap openingat its bottom through which the substrate is conveyed to deposit a layerof uniform thickness on the substrate surface. Depending on theviscosity and thickness of the formulation and the physicalcharacteristics of the substrate, certain measures may be required toprepare the substrate film to promote deposition of a level smoothcoating thereon.

After deposition of the PU formulation, the coated polyester film isexposed either to elevated temperature, electron beam or ultraviolet(UV) light or combination of the foregoing for a time sufficient toactivate cross-linking agent(s) in the formulation and cure the coating.An oven for thermal curing and/or a bank of UV lights may be operativelypositioned downstream of and in line with the take away conveyor of acurtain coater to facilitate continuous curing.

The invention is further described in the following examples which arefor illustration only and not to limit or restrict the invention.Amounts expressed as equivalents are obtained by dividing measuredmolecular weight by the number of measured functional groups permolecule.

The following tests were used to obtain the results tabulated in theExamples

Exposure Stability - Bilayer laminates exposed to a Xenon Weatherometerfor the specified time were checked for yellowness which wascharacterized as yellowness index (YI) and haze (see below). YI wasmeasured using a Hunter D25 Spectrometer. YI less than 16 is deemedacceptable.

% Haze - ASTM D1003-61 (Reapproved 1977) - Procedure A - using aHazemeter, Hunterlab Model D25 from Hunter Associates, Inc., Reston, Va.Less than 4% haze is deemed acceptable as optically clear.

Abrasion Resistance measured as the change in % haze after 100 abrasioncycles: 4 in×4 in (10 cm×10 cm) samples of glass/plasticized PVB/PET/PUbilayer laminates were prepared and the PU layer abraded using aTeledyne Taber Abrader 5130, abrasive wheels No. CS-10F under 500 gweight. The laminates were exposed in Florida at a 45 degree anglefacing south. Less than 4% change in haze is deemed acceptable.

Deformation Recovery - the PU surface of a bilayer laminate sample ofglass/plasticized PVB/PET/PU is deformed at room temperature with a 20mil (0.51 mm) thick blade at a 500 g load for 5 sec. The time requiredfor the deformation to recover is measured. A recovery time of less than24 hours is considered acceptable.

Solvent Resistance - drops of various solvents such as methanol,methylene chloride, chloroform, toluene, etc. are successively held onthe PU surface for 5 sec. and wiped off. The effect on the surface andtime to recover from swelling are noted. Recovery occurring within 12 hris deemed acceptable.

EXAMPLE C-1

This control Example shows the quality after aging of the exposedsurface of a PU coating on a plasticized PVB substrate according to U.S.Pat. No. 4,937,147.

The substrate was a sheet of partial PVB resin from Monsanto Company asSaflex® TG sheet 0.75 mm thick having a hydroxyl content of 18.2%plasticized with 35 parts dihexyl adipate per 100 parts resin. The PUused is disclosed in Example 6 of the '147 patent and it was prepared,applied to and thermally cured at 50° C. on the plasticized PVB sheet asdisclosed in this Example. A bilayer laminate with glass of this PVB/PUstructure was prepared and exposed to 50° C. for an extended period toassess the effect of the PVB plasticizer on the PU coating. After aboutthirty days the exposed PU surface felt lubricious to the touch meaninga decrease in the coefficient of friction due to absorption of thedihexyl adipate by the polyurethane followed by migration to the exposedsurface.

EXAMPLE 1

This is according to the invention.

Optical grade, transparent biaxially stretched polyethyleneterephthalate (PET) film 0.1 mm thick was obtained commercially fromHoechst Celanese as Hostaphan 4400. Without further surfacemodification, a curtain coater as above described was used to coat thisPET film with PU. The support for the PET film during coating wasprepared as follows. A layer of glass on a wood board about 45 cm wideprovided a smooth surface and a porous cloth was stretched over theglass and fastened to the board. A section of the PET film placed on thecloth was then fastened to the board. This assembly was placed in a hotair oven and the temperature increased to 150° C. at which point theheating means immediately shut off. This heat pretreatment relaxedstresses in the PET to draw the film taut under light tension and causeit to lie flat on the support. The underlying porous cloth facilitatedescape of air from beneath the PET film during heat treatment. Thesepreparation procedures may not be necessary with a continuous, fullscale process using a continuous web of film held taut in horizontalposition by an appropriate means such as a moving vacuum plate or tenterframe. The PET film supported as described was then placed on a 45 cmwide conveyor moving at about 19 m/min under the reservoir of a curtaincoater having a gap discharge opening adequate to form a coatingthickness of about 0.25 to 0.5 mm through which issued the following PUformulation.

    ______________________________________                                                           Charge                                                     Component            Equivalents                                                                             Gms.                                           ______________________________________                                        Methylene bis        0.13                                                     (4-cyclohexylisocyanate)                                                      (Desmodur W)                                                                  .sup.1 Polyether triol                                                                             0.0425                                                   .sup.2 Polyether capped triol                                                                      0.0075                                                   .sup.3 Ethoxylated Trimethylol                                                                     0.07                                                     Propane (cross-linker) (ETMP)                                                 Dibutyl tin diacetate 200 ppm                                                 (catalyst)                                                                    Additives:                                                                    .sup.4 Tinuvin 765 (0.25 wt %) 0.5                                            .sup.5 Tinuvin 328 (0.25 wt %) 0.5                                            .sup.6 Irganox 245 (0.25 wt %) 0.5                                            Dow Corning 57 300 ppm                                                        (leveling agent)                                                              ______________________________________                                         .sup.1 Niax LG168, mol wt. = 1000, from Union Carbide Corp., Danbury, Ct,     synthesized by condensing glycerine and propylene oxide.                      .sup.2 Niax 11-27, mol. wt. = 6200 from Union Carbide Corp. Synthesized b     capping the glycerinepropylene oxide adduct with ethylene oxide.              .sup.3 Voranol 234630, Dow Chemical Co.                                       .sup.4 Tinuvin 765: bis(1,2,2,6,6pentamethyl-4-piperidivinyl) sebacate        from Ciba Geigy Corp.                                                         .sup.5 Tinuvin 328: 2(2' hydroxy3',5di-tert-amylphenyl) benzotriazole fro     Ciba Geigy Corp.                                                              .sup.6 Irganox 245: triethylene glycol bis                                    [3(3tert-butyl-4'hydroxy5'methylphenyl) propionate from Ciba Geigy Corp. 

The curtain coated PET film was cured at 70° C. for one hour, which isbelow the temperature range within which stresses in the PET film aresubstantially relieved, to cross-link the PU and provide a tack-free PUsurface After removal from the support, the coated film constituted theprelaminate to be used in a bilayer glazing formed using the previouslydescribed system as will now be specifically described, again withreference to the drawings.

The thermoforming assembly was circular in peripheral shape and housing26 had an inside diameter of 36.8 cm. Support bed 18 was 35.6 cmdiameter and yieldable facing 48 was a molded, room temperaturevulcanized, silicone elastomer with a Shore A Durometer hardness ofabout 65. The upper concave surface of facing 48 was spherical with aradius of curvature of 48.3 cm. The vertical position of bed 18 withinhousing 26 was adjusted so the upper rim of facing 48 was about 0.32 cmbelow the top of sidewall 24 of housing 26. Support bed 18 was fixedconcentrically within housing 26 by tightening positioning screws 64against the inside surface of sidewall 24 of housing 26.

Substrate 102 was a 0.23 cm thick rectangular (about 22.2 cm by 27.9 cm)plate of transparent float glass with rounded corners which had beenoven bent to a spherical curvature of about 48.3 cm radius to closelymatch that of the support member 48. Plate 102 was centrally positionedon member 48, concave side up.

Layered composite 32 comprised a lower layer of plasticized partial PVBof the type and thickness used in Example C-1 having both surfacestextured, in facing contact with the specific prelaminate justdescribed--i.e. 0.05 mm thick PET film coated on its top side with acrosslinked PU layer about 0.25 mm thick. The plasticized partial PVBlayer had eight 6 mm diameter through holes equispaced on a 34 cmdiameter circle. The layered composite was clamped between clamping ring49 and the top face of sidewall 24 forming an air-tight seal around theclamped periphery.

The clamped thermoforming assembly was then placed inside autoclavechamber 12 and the vacuum connection made to manifold 27 (FIG. 1). Theautoclave was sealed and the thermoforming assembly and autoclavechamber simultaneously evacuated while at or near room temperature viavacuum pump 30 to a pressure of 1.33 kPa or less. When evacuation wascomplete, the vacuum connection to the autoclave chamber was closed(valve 37 in FIG. 1) and air slowly admitted to chamber 12 until thepressure in chamber 12 reached about 97 kPa. The pressure differentialdeveloped across composite sheet 32 sharply stretched it into conformingcontact with the curved surface of glass pane 102. Since the spacebetween the clamped composite 32 and the glass substrate and theinterface between sheet 80 and film 82 had been evacuated, there wasnegligible air entrapment during this shaping step. The autoclavepressure was then increased to 1136 kPa over about 10 minutes whiledifferential pressure controller 98 was set to maintain the pressure inthe thermoforming assembly 35-135 kPa below autoclave pressure toprotect against breakage of glass layer 102 or rupture of the compositesheet in the region between the edge of layer 102 and the clamping ring.When the autoclave pressure reached 1136 kPa the pressure difference wasreduced to zero.

Simultaneously with the start of the rise of autoclave pressure,temperature within the autoclave was raised at a rate of 5° C./min.,leveling off at 145° C. and there held for 30 minutes. The autoclave wasthen cooled to room temperature to 5 to 10° C./min., vented over about 5min to atmospheric pressure and opened. The thermoforming assembly wasremoved, the clamps loosened and the glass/composite sheet extracted.Excess plastic was trimmed away leaving a bilayer glazing panel whichincluded plastic layers perfectly conformed to the glass layer withoutvisually apparent wrinkles or optical distortion of objects on one sideof the panel as viewed from the opposite side.

A section of the bilayer panel just described exposed to the same 50° C.elevated temperature used in Example C-1 had a perfectly dry exposedpolyurethane surface after about 30 days indicating that no migration ofthe plasticizer of the partial PVB layer had occurred. Results ofproperty tests on wrinkle-free bilayer glazing panels of this Examplewere as follows:

    ______________________________________                                        Property        Result                                                        ______________________________________                                                      Hrs.                                                            Exposure Stability                                                                            0         4500    5000                                        YI              0.8       -1.52   1.95                                        % Haze          0.88      1.2     0.99                                        Abrasion Resistance                                                                           1.07 @ 0 hrs; 1.67 after                                                      6 mos. Fla.                                                   Deformation Recovery                                                                          15 min                                                        Solvent Resistance                                                                            After initial swelling,                                                       surface returned to                                                           normal when solvent                                                           evaporated                                                    ______________________________________                                    

The above results show the excellent mechanical performance propertiesof the bilayer glazing panels of the invention. YI increase was lessthan 5% after 5000 hrs exposure in the Xenon Weatherometer.

EXAMPLE C-2

This control Example shows the effect on bilayer fabrication of theabsence of polyester film.

The partial PVB-PU plastic laminate of Example C-1 was laminated withglass into a bilayer using the apparatus and procedure of Example 1;polyester film was not used.

Visual examination of bilayers formed revealed significant ripping atthe edge around the periphery of the PU layer (numbered 99 in FIG. 3).When stretched over the edge of the underlying rigid glass layer, thesoft PVB tightly conformed to thickness surface 97 of the glass layer.This excess local extension of the partial PVB undesirably ruptured thePU layer which was strongly bonded directly to and consequently exactlyfollowed the stretching movement of the partial PVB. No such edgerupture of the PU layer was noted in Example 1 where the stabilizinginfluence of the PET film between the partial PVB and PU layers avoidedexcessive local stretching and associated ripping at the edge of the PUlayer.

Moreover, in this Example C-2 the curing temperature of the PU coatinghad to be limited to about 50° C. to avoid wrinkling and distortion ofthe PU surface by shrinkage movement of the thermally sensitiveunderlying partial PVB to which it was chemically bonded. This contrastswith 70° C. in Example 1 in the presence of PET film. Since curing istime-temperature dependent, time can be as low as about 3 min at about110° C. depending on the specific catalyst and concentration used. Suchhigher temperature facilitates commercially desirable reduced curingcycles while still providing a wrinkle-free bilayer product.

EXAMPLE C-3

This illustrates the effect on haze of the PU layer when using certainprior art PU formulations of U.S. Pat. No. 4,937,147 in bilayer glazingpanels of the invention.

A PET-PU laminate was prepared according to the prelaminate formingprocedure of Example 1, except using the prior art formulation ofExample 6 of the '147 patent containing trimethylol propane crosslinkingagent. After curing, the PU coating was so visually milky in appearancethat haze was estimated to be unacceptably greater than 4%. In contrast,when the crosslinker of the PU coating on PET film was ethoxylatedtrimethylol propane, as in Example 1, the haze of the prelaminate andabrasion resistance of the bilayer glazing were well within acceptablequality limits. Similar results are predicted with ethoxylatedtrimethylol propane triacrylate in a formulation tailored for curing byexposure to UV.

Though the apparatus of the invention has been disclosed herein in usewith glass and specific numbers and types of plastic layers, fewer oradditional or alternative functional layers and/or coatings of plasticor other materials can optionally be used as desired in the bilayerstructures being formed. Similarly, instead of glass, it may be possibleto employ an alternative rigid member such as polycarbonate orpolymethyl methacrylate.

When commercial sized systems of the type described herein are used, theprelaminate can be prepared in roll form and conveniently optionallyshipped to another location for local preparation of the bilayer glazingpanel.

The preceding description is for illustration only and is not to betaken in a limited sense. Various modifications and alterations will bereadily suggested to persons skilled in the art. It is intended,therefore, that the foregoing be considered as exemplary only and thatthe scope of the invention be ascertained from the following claims.

We claim:
 1. A wrinkle-free bilayer glazing panel comprisingsequentially:a) a sheet of glass; b) a layer of plasticized partialpolyvinyl butyral; c) a transparent polyethylene terephthalate layer;and d) a layer of cross-linked, self-healing polyurethane whereincross-linking is through the presence of ethoxylated trimethylol propaneor ethoxylated trimethylol propane triacrylate.
 2. The glazing panel ofclaim 1 wherein the sheet of glass has compound curvature and layers b)c) and d) substantially match the compound curvature of the glass sheet.3. The glazing panel of claim 1 or 2 possessing at least the followingproperties measured according to procedures described in thisspecification:i) abrasion resistance of less than 4%; ii) deformationrecovery of less than 24 hours; and iii) less than 5% increase inyellowness index after 5000 hours exposure in a Xenon Weatherometer.